1. Field of the Invention
The present invention relates to medical endoscopic devices, and optoelectronics and in particular a diffuse electromagnetic radiation system located at the distal end of the endoscopic device useful for PhotoDynamic Therapy (PDT).
2. Invention Disclosure Statement
PDT generally relies on exposing a presensitized area to a selected wavelength of activating radiation. The activating radiation typically comes from a diode laser. A diffuse source of radiation can expose a greater area to activation energy and therefore necrotize a larger area. A diffuse light in the human body has conventionally been created with a diffuser or other such attachment to the distal end of an optical fiber. (e.g. U.S. Pat. Nos. 5,431,647; 5,429,635; 5,363,458). The power and light source are both external which requires that the transmission fiber be coupled to the source. The process and mechanisms of coupling often results in a loss of the energy emitted by the source. Therefore, these devices are prone to a loss of efficiency due to coupling problems. Once transmitted, the emitting light from the fiber possesses a narrow NA, limited dispersion and a single axial component. To compensate the light must be diffused with a diffuser. The diffuse light created by scattering is limited by the characteristics of light traveling through the delivery fiber and it is prone to problems such as uneven distribution of light and hotspots.
Endoscopic devices require coupling an electromagnetic radiation source to a fiber so that the radiation may be brought to the desired treatment area. Examples of these devices are the laser endoscopes found in U.S. Pat. Nos. 4,589,404; 5,135,534; 5,540,676. The process of coupling the fiber to the source generally results in a loss of efficiency and power. Also, coupling usually changes the characteristics of the irradiated light from the source. The resultant emission from the fiber is a beam with a small NA, high coherency, and narrow coverage area. The application of PDT with current technology is often a laborious process due to the limited treatment area created by the fiber. A diffuse electromagnetic source ideally would be able to treat a larger area.
An endoscopic device which does place a radiation source at the distal end of the device, is demonstrated in U.S. Pat. No. 5,468,238. The referenced device places a single diode laser at the distal end to maintain spatial coherency and to reduce the loss of power; however, this device is limited in application. If applied for PDT purposes, a narrow light source makes the procedure slow and inefficient. The source of the light is limited to the single diode and therefore is limited to a single wavelength. Flexibility in the types of sources would create broader applicability for a device.
Another device is demonstrated in U.S. Pat. No. 4,852,567. This laser tipped catheter solves the problem of wavelength transmission limitations in silica fibers. By placing a laser crystal at the distal end of the catheter, electromagnetic radiation of one wavelength of light may be converted to another more desired wavelength which is not transmittable through silica fibers. This system still places the initial power source external to the end of the catheter and will suffer from a loss of power due to coupling. The main focus of this invention is the conversion of wavelengths of one radiation source to a different wavelength which a normal optical fiber could not transmit. This invention does not create a diffuse light source. The placement of a laser crystal at the distal end of the fiber does not suggest placement of an actual electromagnetic source at the end of an endoscopic device. This system also limits the area of PDT application due to the narrowly emitted beam.
It would be useful and more efficient to have a source, which provides evenly diffuse radiation and can irradiate a broad area with diffuse radiation. It would also be useful to have a radiation source at the distal end of the endoscopic device to increase efficiency and control. It would be additionally useful to place multiple light sources at the distal end to have the possibility of multiple wavelengths and a greater consistency to the light. The utility of these features would be further increased by circumventing the transmission limitations of fiber optics. The prior art contains only limited solutions to some of these problems. The present invention addresses all these problems.